Weierstrass, Karl Wilhelm Theodor (1815–1897)

Karl Weierstrass was a German mathematician who is considered the father of modern analysis.
Compelled by his father to study law, he instead spent four years at the
University of Bonn, fencing, drinking, and reading math. He left under a
cloud and ended up teaching in secondary schools for many years. In 1854
he published a paper, written 14 years earlier when he was fresh our of
college, in Crelle's Journal, on Abelian functions which completed work that Niels Abel and Karl Jacobi had begun. Its importance was immediately
recognized and Weierstrass was appointed a professor at the Royal Polytechnic
School and a lecturer at the University of Berlin. He went on to give the
first rigorous definitions of limit, derivative, differentiability, and
convergence, and investigated under what conditions a power series will
converge.